A marketing executive wishes to estimate the average monthly sales of a particular brand of gold necklace in local shops. He decides that an estimate, correct with 3% of the population average with a probability of 0.9545(2 standard errors) shall be considered dependable. How big a sample of shops is needed? Assume that based on a previous enquiry, the coefficient of variation of monthly sales of that particular brand of gold necklace is 9%.$\displaystyle \newline Answer: $Here C.V.is 0.09 so $\displaystyle \sigma= 0.09\overline{x}$$\displaystyle S.E._{\overline{x}}= (0.09\overline{x})/\sqrt{n}$$\displaystyle \hspace{45pt}sample size (n)= (2*(0.09\overline{x}/\sqrt{n})/0.03)^2$So the sample size should be 6 times the monthly average sales of that particular brand of gold necklace.